You need to read the channel packaging and publishing guide. There are a few steps involved. You telnet into your development roku box and generate a password. You save that password. Then you'll notice on that "dev web page" exposed by the roku that there's a "Packager" link in the top left. From there is where you create a package. Your roku device generates packages -- they are not the zipped file you first upload. They have an extension of ".pkg" and a guid for the name. After your roku creates the package, you download it to your local computer and upload it to the channel store.
Thanks,
RT